"It is with heavy heart that we inform you that our beloved brother, human rights activist and mayor of the great city passed away this afternoon," Safiya Omari said at a news conference Tuesday evening. "We ask that you pray for his children and family, his friends and for this great city of ours."

The national civil rights community took note when Lumumba became mayor last year of Mississippi's capital city - a place that had seen its share of violence during the civil rights movement. Lumumba, a black nationalist, had worked with mainstream and leftist figures in the civil rights world.

The civil rights community expressed sadness at his passing.

"So heartbroken at the death of Mayor Lumumba," tweeted Sherrilyn Ifill, president of the NAACP Legal Defense and Educational Fund. "A great man, leader and lawyer. His words, 'I am a revolutionary.' "

"You were a man's man and a servant of humanity," tweeted former NAACP president Ben Jealous. "It was an honor to help you free so many wrongfully convicted people."

The native of Detroit was born Edwin Taliaferro and graduated cum laude from Wayne State University Law School. He renamed himself after Patrice Lumumba, the Congolese independence leader, and the Chokwe, an Angolan tribe.

Lumumba's activism began early. On the day after Martin Luther King Jr. died, he took part in a student takeover of a campus building at Western Michigan University, where he was a student. He and others were demanding more black educators and scholarships for black students. He also pushed for more black studies programs at colleges and universities in the Midwest.

He worked with Julian Bond and Dick Gregory as a leader with the Republic of New Afrika, a social movement that proposed an independent black country in the southeastern United States. He also was a target of the FBI's counterintelligence operation.

In 1985, he was part of a legal team that uncovered evidence demonstrating how the FBI targeted and framed late Black Panther Geronimo Pratt. He also defended former Black Panther Assata Shakur, also known as Joanne Chesimard, late rapper Tupac Shakur and represented activists protesting the beating of the late Rodney King.

In 2011, Lumumba successfully persuaded former Mississippi governor Haley Barbour to release the Scott sisters, who served 16 years for an armed robbery they said they did not commit.

There was no official cause of death as of Tuesday night, Lumumba's son, Chokwe Antar Lumumba, told the news media and supporters at St. Dominic's Hospital, where Lumumba was pronounced dead.

"I thank the city of Jackson," Lumumba's son said. "I thank you for giving my father the opportunity to serve the city. It has given him great joy. He has enjoyed working for you."

"He was a great mayor because he was always open and transparent. We didn't agree about everything, but you could talk to him and if you had disagreements you could vent it out," said Jackson Councilman Melvin Priester Jr. "He brought a spirit of openness."

Lumumba hoped to convene a 50th anniversary commemoration of the Mississippi Freedom Summer, when activists traveled to Mississippi to push for voter registration. He often compared some of the poverty in Mississippi to that of a Third World country.

"It is a tragedy for Jackson," Louis Armstrong, the city's deputy director for human and cultural services, said. "We lost a really good man."